1 Field of the Invention
This invention relates generally to a linear motion guide unit, and, in particular, to a ball screw driven linear motion rolling contact guide unit suitable for use in various high precision machining tools and testing apparatuses.
2. Description of the Prior Art
A ball screw driven linear motion guide unit is well known in the art as described, for example, in the Japanese Patent Laid-open Pub. No. 2-298446, and such a guide unit is schematically shown here in FIG. 5. As shown, the guide unit of the above-identified patent application includes a slider B provided with a ball screw mechanism A at the center thereof extending in a longitudinal direction, which is perpendicular to the plane of the drawing. The slider B is received in a channel defined by a rail having a generally U-shaped cross section and is provided with a pair of upper endless circulating paths provided with balls C and another pair of lower endless circulating paths provided with balls D. As well known in the art, each of the endless circulating paths includes a load path section, a return path section E, F and a pair of curved connecting path sections, each connecting the corresponding ends of the load and return path sections. Each of the load path sections is defined by a pair of an inner guide groove formed in a side surface of the slider B and an outer guide groove formed in an inner side surface of the U-shaped rail arranged in an opposed relationship. The ball screw mechanism A generally includes a ball screw which extends through a threaded hole extending through the slider B in a threaded relationship, so that when the ball screw rotates, the slider B is caused to move linearly along its longitudinal axis relative to the rail.
As described above, the ball screw driven linear motion rolling contact guide unit shown in FIG. 5 is capable of providing a relative linear motion between the slider B and the rail under the control of the ball screw mechanism A. However, since there is provided no damping mechanism, the movement of the slider B can be erratic or abrupt in particular when the slider B is set in motion or brought to a halt. Moreover, when the slider B moves back and forth in a reciprocating manner, the movement of the slider B may lack smoothness because of the possible play between the ball screw and the slider B. Besides, the slider B may be set in vibration or rattling motion to cause noises.
In addition, since the return path section E, F of each of the endless circulating paths is located in the slider B at a location horizontally inside of its associated load path section. As a result, mounting holes for use in mounting desired objects on the slider B must be provided at a location between the load and return path sections. Thus, there is a significant limitation in the degree of freedom in mounting an object on the slider B.